Human epidermal growth factor receptor-2 and estrogen receptor expression, a demonstration project using the residual tissue repository of the Surveillance, Epidemiology, and End Results (SEER) program.

BACKGROUND: In 2001, the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program established Residual Tissue Repositories (RTR) in the Hawaii, Iowa, and Los Angeles Tumor Registries to collect discarded tissue blocks from pathologic laboratories within their catchment areas. To validate the utility of the RTR for supplementing SEER's central database, we assessed human epidermal growth factor receptor-2 (HER2) and estrogen receptor expression (ER) in a demonstration project. MATERIALS: Using a prepared set of tissue microarrays (TMAs) residing in the Hawaii Tumor Registry (HTR), we performed standard immunohistochemistry. Breast cancers in the TMA were diagnosed in 1995, followed through 2006, and linked to SEER's main database. RESULTS: The TMA included 354 cases, representing 51% of 687 breast cancers in the HTR (1995). The HTR and TMA cases were similar with respect to patient demographics and tumor characteristics. Seventy-six percent (76%, 268 of 354) of TMA cases were HER2+ and/or ER+, i.e., 28 HER2+ER-, 12 HER2+ER+, and 228 HER2-ER+. There were 67 HER2-ER- cases and 19 were unclassified. Age distributions at diagnosis were bimodal with dominant early-onset modes for HER2+ER- tumors and dominant late-onset modes for HER2-ER+ breast cancers. Epidemiologic patterns for concordant HER2+ER+ (double-positive) and HER2-ER- (double-negative) were intermediate to discordant HER2+ER- and HER2-ER+. CONCLUSION: Results showed contrasting incidence patterns for HER2+ (HER2+ER-) and ER+ (HER2-ER+) breast cancers, diagnosed in 1995. Though sample sizes were small, this demonstration project validates the potential utility of the RTR for supplementing the SEER program.

Farnesyl transferase inhibitors: the next targeted therapies for breast cancer?

The ras family of proto-oncogenes are upstream mediators of several essential cellular signal transduction pathways involved in cell proliferation and survival. Point mutations of ras oncogenes result in constitutively active Ras and have been shown to be oncogenic. However, ras activation can occur in the absence of ras mutations secondary to upstream receptor activation. The first important step in Ras activation is farnesylation by farnesyl transferase, and inhibitors of this enzyme have been demonstrated to inhibit Ras signaling, and have anti-tumor effects. However, it is now clear that farnesyl transferase inhibitors (FTIs) have activity independent of Ras, most likely due to effects on prenylated proteins downstream of Ras, which explains their activity in several malignancies, including breast cancer, where ras mutations are rare. Several FTIs are in clinical development for the treatment of solid tumors. Preclinical evidence suggests that FTIs can inhibit breast cancers in vitro and in vivo, and a phase II trial of the FTI, R115777, in patients with advanced breast cancer produced encouraging results. Based on prior successful outcomes with agents targeting the estrogen and epidermal growth factor receptor pathways in breast cancer, the FTIs, used alone or more likely with other agents, may be the next exciting targeted therapy in breast cancer.

Effects of the new selective estrogen receptor modulator LY353381.HCl (Arzoxifene) on human endometrial cancer growth in athymic mice.

PURPOSE: Arzoxifene (Arzox) is a novel benzothiophene analogue with selective estrogen receptor modulator activity similar to raloxifene. Arzox is being developed as a treatment for breast cancer and has a predominantly antiestrogenic effect on the rodent uterus. Our objectives were to verify whether the novel selective estrogen receptor modulator, Arzox, can be a good first-line agent and also be effective at controlling the growth of endometrial cancer after exposure to tamoxifen (Tam). EXPERIMENTAL DESIGN: We compared the effects of Tam and Arzox on the growth of estrogen responsive ECC-1 endometrial cancer cells in vitro, and we determined their antitumor effects on ECC-1 and EnCa101 endometrial carcinoma growth in athymic mice. RESULTS: We observed that estrogen receptor protein expression is down-regulated by Arzox to the same extent as raloxifene, whereas 4-hydroxytamoxifen, the active metabolite of Tam, does not affect estrogen receptor protein levels. Tam and Arzox inhibit the growth of Tam-naïve ECC-1 tumors in athymic mice. However when Tam-stimulated or estrogen-stimulated (which had been treated with Tam previously) EnCa101 endometrial tumors were treated with Tam or Arzox, we observed a stimulatory effect of both compounds in these models. CONCLUSIONS: The results indicate that Arzox may be a good first-line agent, but it may be ineffective at controlling the growth of endometrial cancer after exposure to Tam. Our data suggest that Arzox stimulates endometrial tumor growth to at least the same extent as Tam, thereby suggesting a limited role as a second-line agent for the patient on Tam who develops occult endometrial cancer.

Selective estrogen-receptor modulators in 2001.

Tamoxifen (Nolvadex), a selective estrogen-receptor modulator, or SERM, is currently the endocrine therapy of choice for all stages of hormone-responsive breast cancer. Only tamoxifen has been approved by the US Food and Drug Administration to reduce the incidence of breast cancer in high-risk women. Despite tamoxifen's antiestrogenic effects in breast tissue, it exhibits paradoxical estrogenic effects in other tissues in the body. These effects result in the maintenance of bone mineral density, but a three- to fourfold increase in endometrial cancer in postmenopausal women. Additionally, tamoxifen can result in troublesome hot flashes and serious thromboembolic events. For this reason, current research is focusing on new agents that may maintain the beneficial effects of tamoxifen while reducing its adverse effects. Raloxifene (Evista) is another SERM, approved for the prevention of osteoporosis in postmenopausal women and now being compared with tamoxifen in an ongoing breast cancer prevention trial. Like tamoxifen, raloxifene is associated with hot flashes and thromboembolic events, but its association with the risk of endometrial cancer is unknown. A number of new SERMs are in preclinical or clinical development in an attempt to improve upon the safety profile of tamoxifen. Additionally, selective aromatase inhibitors are being examined in the early breast cancer setting.

Analysis of cross-resistance of the selective estrogen receptor modulators arzoxifene (LY353381) and LY117018 in tamoxifen-stimulated breast cancer xenografts.

PURPOSE: Cross-resistance is the primary issue facing the evaluation of new antiestrogens to treat metastatic breast cancer because they may be tested, initially, in populations of patients that have failed long-term adjuvant tamoxifen (Tam) therapy. EXPERIMENTAL DESIGN: We have tested the benzothiophene derivatives, arzoxifene (Arzox; LY353381) and LY117018 in two models of Tam-stimulated tumor growth derived from either MCF-7 (M. M. Gottardis and V. C. Jordan, Cancer Res., 48: 5183-5187, 1988) or T47D (J. MacGregor Schafer et al., Clin. Cancer Res., 6: 4373-4380, 2000) breast cancer cells. RESULTS: Using the MCF-7:Tam model, we found that both Arzox and LY117018 (1.5 mg/day) resulted in tumor growth and, therefore, were partially cross-resistant with Tam. Next, using the T47D:17beta-estradiol (E(2)) model, we compared the antiestrogenic/antitumor properties of Arzox and LY117018 and determined that neither Arzox nor LY117018 caused T47D:E(2) tumor growth after 21 weeks. In addition, we determined that long-term treatment does not result in failure and subsequent development of transplantable Arzox- or LY117018-stimulated tumors. To establish whether Arzox and LY117018 are cross-resistant in T47D:Tam tumors, mice were treated with Arzox or LY117018 (1.5 mg/day), and, again, we found that neither resulted in the growth of transplantable tumors. Lastly, we showed that Arzox and LY117018 were only partially able to compete with postmenopausal E(2) (0.3 cm silastic capsule) in T47D:Tam tumors. However, when T47D:E(2) tumors were treated for 7 days instead of 5 days, both Arzox and LY117018 were more effective. CONCLUSIONS: Arzox is not cross-resistant with Tam in the T47D athymic mouse model but does exhibit cross-resistance in the MCF-7 model.

Tamoxifen to raloxifene and beyond.

Tamoxifen, a selective estrogen receptor modulator (SERM), is the treatment of choice for all stages of hormone-responsive breast cancer and has been shown to prevent breast cancer in high-risk women. Despite acting as an antiestrogen on the breast, tamoxifen has partial estrogenic effects on other target tissues. These partial estrogen agonistic actions produce beneficial effects on bones and the lipid profile in postmenopausal women. However, tamoxifen is associated with an increase in endometrial cancer. Additionally, its antiestrogenic effects in the central nervous system result in hot flashes in postmenopausal women. Raloxifene is another SERM approved for the prevention of osteoporosis in postmenopausal women. Like tamoxifen, raloxifene appears to prevent breast cancer in high-risk women and has not, to date, been noted to increase the incidence of endometrial cancer. The Study of Tamoxifen and Raloxifene will compare the effects of the two agents on breast cancer prevention and endometrial cancer risk. A number of new agents are being developed for breast cancer treatment and prevention and osteoporosis prevention. These include other SERMs, selective estrogen receptor downregulators (SERDs), and aromatase inhibitors. It is hoped that one of these new agents will be the ideal agent, acting as an antiestrogen on breast and endometrium while having estrogenic effects on bones, the lipid profile, and the central nervous system. Semin Oncol 28:260-273.

Rapid development of tamoxifen-stimulated mutant p53 breast tumors (T47D) in athymic mice.

MCF-7 cells are used routinely to study tamoxifen-stimulated drug resistance in vivo. However, unlike MCF-7 cells, T47D cells express mutant p53 protein and lose the estrogen receptor (ER) during long-term estrogen deprivation in vitro [Pink et al., Br. J. Cancer, 74: 1227-1236, 1996 (erratum, Br. J. Cancer, 75: 1557, 1997)]. As a result, T47D tumors may respond differently from MCF-7 tumors to long-term tamoxifen treatment. Ovariectomized athymic mice were given injections bilaterally with T47D cells (5 x 10(5)) into the mammary fat pads. A rapidly growing estradiol responsive tumor (T47D:E2) was established and 0.5 mg of tamoxifen given daily blocked estrogen-stimulated growth. In subsequent experiments, low doses of tamoxifen (0.17 mg or 0.5 mg) did not produce tamoxifen-stimulated tumors at 14 weeks, whereas high-dose tamoxifen (1.5 mg) consistently produced tamoxifen-stimulated tumors (T47D:Tam; 17 tumors/20 sites) at 8 weeks. In contrast, 1.5 mg of tamoxifen produced tamoxifen-stimulated MCF-7 tumors (MCF-7: Tam2) at a slower rate (20 weeks) and less consistently (14 tumors/26 sites). When the T47D:Tam tumor was passaged, it grew maximally with either 1.5 mg of tamoxifen or a 1-cm estradiol (premenopausal levels) capsule, and similar results were obtained with MCF-7:Tam2 tumors. Interestingly, when T47D:Tam tumors were treated with the 0.5 mg of tamoxifen, tumors grew only to 50% maximum. All of the tumors originating from MCF-7 and T47D cells expressed ER at similar levels; therefore, tamoxifen did not select for an ER-negative tumor. In conclusion, we have shown that tamoxifen-stimulated T47D p53 mutant tumors can be developed rapidly with high-dose therapy (1.5 mg daily). The results from this model provide new opportunities to investigate the rapid development of drug resistance to adjuvant tamoxifen in patients with mutant p53 breast tumors.

Antitumor action of physiological estradiol on tamoxifen-stimulated breast tumors grown in athymic mice.

The estrogen receptor (ER)-positive MCF-7 breast cancer cell line can be transplanted into athymic mice and grown into tumors with estradiol (E2) support. Tamoxifen (TAM) blocks E2-stimulated tumor growth; however, continuous TAM treatment results in transplantable tumors within a year that will grow with either E2 or TAM (M. M. Gottardis and V. C. Jordan, Cancer Res., 48: 5183-5187, 1988). Although this model may represent the development of TAM resistance for the treatment of advanced breast cancer, no laboratory model exists to study the exposure of breast cancer to 5 years of adjuvant TAM therapy. We have addressed this issue and report the development and characterization of two tumor lines, MCF-7TAM and MT2, which have been serially transplanted into TAM-treated athymic mice for >5 years. The MCF-7TAM tumor rapidly regresses in response to E2 and then about 50% of tumors regrow in response to E2. Interestingly, tumor regression does not occur if TAM treatment is stopped, probably because E2 levels are too low in ovariectomized athymic mice. The development of the antitumor effect of E2 was documented for MT2 tumors over a 1-year period; TAM-stimulated tumor growth was retained, but E2 caused progressively less of a stimulatory effect. Most importantly, E2-stimulated tumors that regrew after initial tumor regression in both MCF-7TAM and MT2 lines were again responsive to TAM to block E2-stimulated growth. Unlike MCF-7 tumors, the MT2 tumor line contains a single point mutation, Asp351Tyr, in the ER, which was retained after the development of E2-stimulated regrowth. The mutation is associated with increased estrogen-like actions for the TAM-ER complex (A. S. Levenson et al., Br. J. Cancer, 77: 1812-1819, 1998), but we conclude that the mutant ER is not required for TAM resistance. On the basis of the new breast cancer models presented, we propose a cyclic sensitivity to TAM that may have important clinical implications: (a) it is possible that a woman's own estrogen may produce an antitumor effect on the presensitized micrometastatic disease after 5 years of TAM. Long-term antitumor action occurs because the drug is stopped, but resistance accumulates and tumors start to grow if adjuvant therapy is continued; and (b) although in the clinic TAM-resistant tumors respond to second-line therapies that cause estrogen withdrawal, e.g., pure antiestrogens or aromatase inhibitors, estrogen therapy may also be effective and return the tumor to TAM responsiveness. In this way, a hormone-responsive tumor may be controlled longer in the patient with advanced disease.

Cross-resistance of triphenylethylene-type antiestrogens but not ICI 182,780 in tamoxifen-stimulated breast tumors grown in athymic mice.

The triphenylethylene antiestrogens, idoxifene (Idox) and toremifene (Tor), are structurally related analogues of tamoxifen (Tam) and were developed to improve the therapeutic index for advanced breast cancer patients. However, the issue of cross-resistance with Tam for these new agents is critical for clinical testing because the majority of breast cancer patients have already received or failed adjuvant Tam. The goal of this study was to determine the effectiveness of Idox as an antitumor agent in three models of Tam-stimulated breast cancer in athymic mice and compare the results with the actions of Tor and ICI 182,780 in a Tam-stimulated MCF-7 tumor model. We first compared the activities of Tam and Idox in the 17beta-estradiol (E2)-stimulated MCF-7 tumor line MT2:E2. Tam and Idox reduced E2-stimulated growth by 65-70% (week 9: P = 0.0009 for Tam, P = 0.0005 for Idox versus E2 alone). However, Tam (1.5 mg daily) and Idox (1.0 mg daily) both produced T47D breast tumors in athymic mice during 23 weeks of treatment (12 tumors/22 sites and 15 tumors/18 sites, respectively). Tam and Idox stimulated tumor growth equally in two different Tam-stimulated MCF-7 models and in a T47D model. Tor was completely cross-resistant with Tam in the MCF-7 tumor model, which implied that neither Idox nor Tor would be effective as a second-line endocrine therapy after Tam failure and may offer no therapeutic advantages over Tam as adjuvant therapies. In contrast, ICI 182,780, a pure antiestrogen currently being tested as a treatment for breast cancer after Tam failure, had no growth-stimulatory effect on the MCF-7 Tam-stimulated breast tumor line. This agent may provide an advantage as an adjuvant therapy and increase the time to treatment failure.

Effects of the antiestrogens tamoxifen, toremifene, and ICI 182,780 on endometrial cancer growth.

BACKGROUND: Tamoxifen has been shown to promote the growth of human endometrial tumors implanted in athymic mice, and it has been associated with a twofold to threefold increase in endometrial cancer. Toremifene, a chlorinated derivative of tamoxifen, and ICI 182,780, a pure antiestrogen, are two new antiestrogens being developed for the treatment of breast cancer. The effects of these drugs on endometrial cancer are currently unknown. Our objective was to evaluate the effects of toremifene and ICI 182,780 on the growth of human endometrial cancer in athymic mice. METHODS: Athymic, ovariectomized mice were implanted with human endometrial tumors and treated with estrogen, tamoxifen, or the new antiestrogens. RESULTS: The effects of tamoxifen and toremifene on the growth of either tamoxifen-stimulated or tamoxifen-naive endometrial tumors in athymic mice were not substantially different. ICI 182,780 inhibited the growth of tamoxifen-stimulated endometrial cancer, in both the presence and the absence of estrogen. CONCLUSIONS: Toremifene and tamoxifen produce identical effects in our endometrial cancer models. Therefore, it is possible that toremifene, like tamoxifen, may be associated with an increased incidence of endometrial cancer. In contrast, ICI 182,780 inhibited tamoxifen-stimulated endometrial cancer, both in the presence and in the absence of estrogen, suggesting that this drug may be safe with regard to the endometrium, even if it is used following tamoxifen, and that it may not result in an increased incidence of endometrial cancer. Indeed, it is even possible that ICI 182,780 may prove useful as an adjuvant agent in early stage endometrial cancer.

Laboratory models of breast and endometrial cancer to develop strategies for antiestrogen therapy.

Laboratory models for breast and endometrial cancer have had an enormous impact on the clinical development of antiestrogens. Results from the DMBA-induced rat mammary cancer model has provided the scientific principles required to evaluate long-term adjuvant tamoxifen therapy. Similarly, the athymic mouse model allowed the identification of clinically relevant mechanisms of drug resistance to tamoxifen and a model system to test new agents for cross resistance. Additionally, the endometrial cancer model has allowed the identification of agents that cause a slight increase in the risk of endometrial cancer long before the data would have be available from clinical studies. However, it should be stressed that this model is really only relevant for agents to be tested as preventives in normal women. The risks of developing endometrial cancer during tamoxifen therapy are slight compared with the survival benefit in controlling breast cancer.Finally the discovery of the carcinogenic potential of tamoxifen in the rat liver, 20 years after it was first introduced into clinical practice, raises an interesting issue. If the studies of liver carcinogenicity had been completed and published in the early 1970's there would be no tamoxifen and tens of thousands of women with breast cancer would have died prematurely. In fact there would have been no incentive to develop new agents as alternatives to tamoxifen or following tamoxifen failure. Most importantly, we would not have any knowledge about the target-site or selective actions of antiestrogens. All the current interest in selective estrogen receptor modulators (SERMs) is based on the huge clinical data base obtained by studying tamoxifen. The success of tamoxifen as an agent that preserves bone density, lowers cholesterol and prevents contralateral breast cancer(43) has become a classic example of a multimechanistic drug. These concepts have acted as a catalyst to develop new agents for new applications. The laboratory studies of raloxifene(44-46)) provided the scientific rationale for the use of raloxifene as a preventive for osteoporosis(47)) but with the goal of preventing breast cancer in post-menopausal women(48,49)) (Fig 5). It is clear that the close collaboration between laboratory and clinical research has revolutionized the prospects for women's health care in the 21st century.